The invention relates to a conveyor mat built up of intermediate modules and end modules, made in one piece of synthetic material, the width of the intermediate modules being substantially twice the width of the end modules, with the modules, viewed in the longitudinal direction of the mat, being staggered, each module consisting of a plurality of substantially equally spaced-apart hinge plates, each extending over substantially the entire length of the module and each having hinge loops at the two ends thereof, the hinge plates of a module being coupled to each other by means of a rib located between the two ends, the ends of the hinge plates on a longitudinal side of a module being located between the ends of the hinge plates of a module adjacent in the longitudinal direction of the mat, the hinge loops of the two modules being substantially in alignment and coupled to each other by means of a hinge pin extending through the openings of the hinge loops, there being provided means for locking the hinge pin relative to the modules.
Such a conveyor mat, built up of modules, is disclosed in European Patent Document 380201 and is for instance used in the packaging industry, in bottling plants and the like, wherein the mat may have a relatively large width, up to some meters, and is designed as an endless conveyor mat, which at the beginning and the end of a conveying path is guided over sprocket wheels arranged across the width of the conveyor. The modules of which the mats are built up exist in various length dimensions; for instance, a length of 1 inch and of 2 inches is very conventional. For a module having a length of 1 inch, it has already been proposed in the above-mentioned European patent application to drive the module at the connecting rib of the hinge plates, for which purpose the teeth of the sprocket wheels are provided with a slot-shaped opening, in operation meshing with the rib on two sides. For particular applications, it is desirable that mats can be used whose modules have a length which is even slighter than that of the known modules, for instance a length of 0.5 inch. Such very short modules have the advantage that the modules at the end of the mat, where they are passed around a sprocket wheel, are only slightly inclined to raise from the plane of the mat due to the sprocket wheel meshing with the module, the so-called polygon effect. This polygon effect is disadvantageous, because it may cause the articles conveyed over the mat to fall down or at least obtain an unstable position. A further advantage of using very short modules is that the diameter of the sprocket wheels can be very small, which at the transition between two adjacent mats necessitates only a short "dead plate", the plate over which the articles are moved from one mat to the other. It is desired that a short dead plate has, in the conveying path, as few portions as possible that do not actively contribute to the conveyance.
To provide such modules of a slight length with sufficient strength, it is obvious that a minimal material thickness around the hinge loops, a minimal thickness of the rib and a minimal diameter of the hinge pin and hence of the hinge loops are required. It has been found that it is impossible to construct a module having such minimal material thicknesses and at the same time a length of, for instance, 0.5 inch in the same manner as the modules known from European Patent Document 380201, because the free space remaining between the rib of a module and the hinge loop located opposite thereto is too small for the drive tooth of a sprocket wheel to mesh therewith.
It is observed that a person skilled in the relevant field of expertise does not define the length of a module as the length of a single, separate module, but as the distance between the centers of the hinge pins which couple a module to adjacent modules. This is only logical, because for modules coupled with each other this distance determines the characteristics of the mat. In the case of oval hinge loops, this distance may slightly differ from the distance between the centers of the hinge loops of one module.
The object of the invention is to provide a chain mat whose modules are of such configuration that in spite of the very slight length of the modules it is still possible to move the chain mat forward and backward by means of a sprocket wheel.